To get a typical printer's output to match a standard other than the standard that the inkset was designed to match (assuming it was designed to match a standard), a method called color profiling is typically used. Color profiling is an attempt to characterize the printer's colorimetric reproduction characteristics given a specific set of inks, media, and environmental conditions and use this information along with color correction data that attempts to get the printer's output to match a standard.
To characterize a printer, a test chart is printed consisting of a finite set of color patches. The chart is then measured using a calorimeter or spectrophotometer to determine the colorimetry of each of the patches. The colorimetric data is then used to derive a model to map data from one space (CMYK printer counts) to another (XYZ). It is then the job of the color management engine to use the printer model to predict the amount of CMYK ink required to reproduce a given color. This is commonly done using multi-dimensional look-up tables. This is shown schematically in FIG. 1.
Printer characterization techniques most often attempt to reproduce specified colorimetric values (XYZ or LAB) of an original image, also known as a metameric reproduction. This requires an assumption about the viewing illuminant, for example, CIE Illuminant D50. If the viewing illumination of the final print is different than the assumed illuminant, as is often the case, then the resulting viewed LAB values will most likely be different than the requested values even if the characterization technique had no other errors (e.g., interpolation). Thus a mismatch occurs between the reproduction and original values.
In order to account for this, some printers and/or characterization procedures allow the user to specify a illumination by selecting one from a list of illuminations or use a digital sensor affixed to the printer for sensing of ambient illumination. It is desirable to modify the characterization table based on the viewing illumination or to characterize for several possible viewing illuminations and use the appropriate one depending on where the printer is situated or where the prints will be viewed.
What is needed in the arts is a method which allows users to quickly determine their approximate viewing illumination without incurring additional expense or requiring certain expertise particularly with respect to colors not being accurate because the wrong viewing illuminant was assumed for the printer characterization.